science

Hydropower development is booming, with controversial projects unfolding across the Americas, Africa, Asia and Europe.

Though often presented as a green renewable energy option, dams can cause a litany of negative impacts: disrupting the downstream flow of nutrients, interrupting aquatic migration routes and harming fisheries. They flood forests, destroy habitat and increase the release of greenhouse gases as vegetation decomposes. Dams also displace human communities — submerging homes and indigenous territories.

A new study adds another impact to the list, one that is widespread but has so far been overlooked by dam developers: “extinction debt” — the incremental but inexorable loss of species and diminishment of biodiversity over time on islands created by reservoirs.

Hydropower developers have long claimed reservoir islands as quality habitat and as viable conservation areas — both assertions are false, according to the new research.

A global evaluation of reservoir islands

The study, led by Isabel Jones at the UK’s Stirling University, collated biodiversity data from 100 studies of reservoir islands — with time since habitat isolation ranging from 1 to 92 years — at 15 dams in North, Central and South America, Europe, and Asia.

In more than 75 percent of cases studied, dams had an overall negative impact on reservoir island species, affecting factors such as species population density, ecological community composition, and species behavior.

Thousand Island Lake in China, the result of a dam built in the 1950s on the Xin’an River, was one of 15 dams worldwide included in a recent study that concluded that reservoir islands should not be counted as conservation areas by developers. Photo by Bryan Ong on Flickr, under a Creative Commons CC BY-NC-ND 2.0 license

For as long as people have lived in the Amazon, turtles have likely been on the menu. But what was once low-impact subsistence hunting escalated dramatically after the arrival of Europeans. From the 1700s onward, demand for turtle eggs and meat skyrocketed. And the eggs weren’t just for eating: estimates suggest that more than 200 million eggs were harvested for both consumption and oil, fuelling lamps across Europe for two centuries.

This overexploitation led to such dramatic population declines that the Brazilian government eventually stepped in, launching the ambitious Amazon Turtle Program in 1979 — an on-going initiative that has so far protected 70 million turtle hatchlings across the Brazilian Amazon, with the intent of conserving vulnerable species.

But while that program continues to work toward a sustainable future for turtle populations —and for the people who still see chelonians as an important source of protein — three more recent threats loom over Amazonian turtle species: the illegal wildlife trade, widespread hydropower dam construction, and mercury contamination.

The Giant Amazon River Turtle (Podocnemis expansa) is the largest species of neotropical freshwater turtle, and is found throughout the Amazon basin. Overexploited for centuries, the species is making a comeback thanks to conservation initiatives. Photo courtesy of Camila Ferrara

An estimated 1,500 orangutans now live in rescue and rehabilitation centers located across Sumatra and Borneo. As habitat loss due to deforestation and forest fires continues, these institutions are struggling to keep up with demand.

Release into the wild is the ultimate, urgent, goal for most of these animals, but a new study warns that there could be serious genetic implications for the offspring of reintroduced animals — and orangutan populations in general — if those rescued from one region are released into a different region.

The study, led by primatologist Graham Banes, examined the genetic consequences when orangutans from different, divergent, subspecies interbreed. Borneo’s three recognized subspecies — from three distinct regions — are thought to have diverged from each other 176,000 years ago, meaning that hybridization between them may result in negative genetic effects. If hybrid offspring reproduce, combinations of genes that were beneficial for one lineage can be disrupted, resulting in poor health and reduced reproductive success, the researcher said. These effects, known as “outbreeding depression,” could threaten the survival of individuals and populations in the long-term.

Amazonia’s surge in hydropower development threatens numerous species with extinction, and puts unique habitats at risk, warns a recent study.

River dolphins, giant otters, turtles, fish, birds and monkeys will all have their habitats altered by hydroelectric dams, with some species likely to be completely wiped out, says an international team of biologists that looked at all impacts associated with 191 existing Amazon dams, as well as the 246 dams being planned or under construction.

What’s more, the researchers identified a network of negative interactions between dam construction, mining, climate change, human migration, and biodiversity and ecosystem services which illustrates how impacts can cascade in multiple, devastating ways.

In environmental terms, the most obvious and direct impact of dams reported by the study are on water flow and connectivity. Nutrients that flow downstream from the Andes are interrupted by dams; flood pulses that form a vital part of many species’ lifecycles are modified by the reservoirs and flow patterns that dams create and control; habitat complexity is lost; and species such as river dolphins become isolated in the stretches of river between hydropower developments, which leaves smaller sub-populations vulnerable to decline.

To read the full article, orginally published on Mongabay, click here.

River turtles in Colombia. Turtles, dolphins and otters are among the aquatic species threatened by dam construction, but risks extend to birds, bats and terrestrial animals too. Photo by Rhett A. Butler

Among the myriad impacts climate change is having on the world, one in particular may come as a surprise: heightened atmospheric CO2 levels might be adversely affecting the nutritional quality of the food you eat. As carbon dioxide in the atmosphere continues to increase, you could end up eating more sugar and less of important minerals such as zinc, magnesium and calcium — without even realizing it. Those effects could also be reverberating up the food chain and altering ecosystems in as yet poorly understood ways.

For plants, a rise in atmospheric carbon dioxide actually boosts productivity by stimulating photosynthesis. They make more carbohydrate and grow larger — seemingly a good thing. But because other nutrients don’t increase and can’t keep pace with the augmented carbohydrate, this potential boon to our food supply isn’t all that it seems: plants end up having a higher carbohydrate to protein ratio, and relatively lower concentrations of minerals.

Put simply: atmospheric carbon dioxide acts as a sort of fertilizer to grow bigger, leafier plants, but those larger broccolis and lettuces actually contain less nutritional value per portion than their predecessors grown in the preindustrial, pre-fossil fuel world.

And that could be a problem for the world’s already malnourished people, for bees seeking protein-rich pollen so they can safely overwinter, and for ecosystems that could be thrown out of balance by changes in plant nutrition.

The human implications of these ongoing changes to our food supply came under the spotlight in April when the US Global Change Research Program (USGCRP) published a major report on the impact of climate change on human health. One of its key findings was that rising carbon dioxide will reduce the nutritional quality of food.

Rice fields in Kashmir, India. Staple crops such as rice and wheat are forecast to become less nutritious as a result of increasing carbon dioxide levels in the atmosphere. Photo courtesy of sandeepachetan.com travel photography on Flickr under CC BY-NC-ND 2.0 license

Imagine a fish isolated in an Amazonian lake — part of the vast freshwater ecosystem of the Amazon basin, an ever-changing network of rivers, lakes and floodplains that extends to 1 million square kilometers (386,102 square miles).

Now imagine that isolated fish as water levels rise during the wet season, and floodplains vanish beneath up to 15 meters (49 feet) of water. The fish — once restricted by the lake’s edge — swims freely into the flooded forest and mingles with others of its kind from elsewhere.

For thousands of years, isolated fish populations across the Amazon have likewise played a game of musical chairs: intermixing between flooding water bodies, migrating short and vast distances between lakes and along river channels, and then as the waters receded, forming new lake and river populations.

This connectivity — with the genetic mixing it affords — is vital for healthy fish populations, but is extremely vulnerable to changes in the annual “flood pulse” that inundates forests.